Traditionally, cable networks were based on coaxial cable that was laid up to and installed inside various subscriber premises. However, with the growth of the Internet and desire to provide high-speed Internet access and/or on-demand programming, it is now common for sections of the coaxial cable to be upgraded to lower loss fiber. Accordingly, these cable networks are often referred to as Hybrid Fiber Coaxial (HFC) networks. In a typical HFC network, data carried by optical signals is transmitted over long distances of optical fibers, and then transformed to radiofrequency (RF) signals and transmitted over CATV cable. For example, in many HFC networks optical signals from the master headend are transmitted on trunklines that go to several distribution hubs, from which multiple optical fibers fan out to carry the optical signal to boxes called optical nodes in local communities. At the nodes, the optical signals are transformed to RF signals and carried by various local coax cables to different subscriber premises.
Data Over Cable Service Interface Specification (DOCSIS) is the international telecommunications standard developed by CableLabs, which allows transparent, bi-directional, high-speed data transfer over an existing cable TV (CATV) system. A DOCSIS system typically includes a cable modem (CM) located at one or more subscriber premises and a cable modem termination system (CMTS) located at a headend or hub. For example, one or more CMTSs, which access a backbone network (such as the Internet), are often located in a headend system that is generally stored within a central office of a cable service provider, while a plurality of CMs are located at different subscriber premises. The transparent, bi-directional, transfer of Internet Protocol (IP) traffic between the CMTSs and the CMs is achieved via the cable network. The communication direction from the CMTS to the CMs is referred to as the downstream direction, whereas the communication direction from the CMs to the CMTS is referred to as the upstream direction.
Referring to FIG. 1, there is shown a schematic diagram of one embodiment of a HFC network. The HFC network 10 includes a headend 2 coupled to a node 8 via fiber optic cable 3 and coaxial cable 7. The fiber optic cable 3 and coaxial cable 7 convey information (e.g., television programming, Internet data, voice services, etc.) between the headend 2 and the plurality of subscriber premises 28a, 28b, 28c served by the distribution node 8. In general, the headend 2 will either be a large central headend or a smaller headend (e.g., a distribution hub). Note that only one node 8 and three subscriber premises 28a/28b/28c of the HFC network are illustrated for exemplary purposes. In general, the HFC network 10 will include more than one node and more than three subscriber premises. For example, each hub in a typical HFC network will serve over one hundred nodes, while each node provides up to 200 homes with DOCSIS service. A city the size of Indianapolis may have five or six hub sites.
The CMTS 4, which includes a network interface (e.g., an Ethernet interface) to servers 23 via the network 1, provides downstream control and data delivery via the downstream signal combiner 24 and upstream control and data reception via the upstream signal splitter 25. The signal combiner 24 couples the downstream signal of the CMTS 4 with the other signals (e.g. TV, Test, Telephony etc.). The output of the signal combiner 24 is connected to a fiber transceiver node 26, which converts the combined downstream signal suite from RF signals to optical signals, and delivers the combined optical signal suite to a remote location via the fiber optic link 3. The downstream optical signals are converted to RF signals at the transceiver node 27, which is also optically coupled to the optical fiber link 3. The RF signals from the transceiver node 27 are delivered to different subscriber premises 28a, 28b, 28c via the distribution node 8.
The distribution node 8 is part of the CATV plant 21. The CATV plant 21 also includes coaxial cable 7 connected to the plurality of subscriber premises 28a, 28b, 28c. As is known in the art, each of the subscriber premises 28a, 28b, 28c may be a residence, a commercial establishment, or an industrial establishment. Each subscriber premises 28a, 28b, 28c includes customer premises equipment (CPE) 5, which is any type of electronic equipment located on the customers premises and connected to the network. For example, in one embodiment CPE 5 includes one or more cable modems (CMs), telephones, routers, switches, residential gateways, set-top boxes, fixed mobile convergence products, etc. Referring to FIG. 2, there is shown an embodiment wherein the CPE 5 includes a VoIP analog terminal adaptor 6a for a telephone 4a, a CM 6b for a computer 4b, and a set-top box 6c for a television 4c. Data and control signals are transmitted from the CMTS 4 on downstream channels and are detected and demodulated by each of the CPE components 6a, 6b, 6c. The CPE components 6a, 6b, 6c also transmit upstream signals, including VoIP conversations, internet uploads, on-demand requests, etc. to the CMTS 4. Accordingly, CPE devices are commonly termed terminal equipment devices.
Although the coaxial cables and connectors within the cable plant 21 are typically shielded to prevent over-the-air signals from affecting the signals carried within the coaxial cable, electromagnetic fields often leak therethrough. Egress, which is defined as the passage of signal carried within the coaxial cable into the outside world, can result in a weaker signal at the end of the cable and radio frequency interference to nearby devices. Ingress, which is defined as the passage of an outside signal into the coaxial cable, can dramatically reduce the reliability of upstream data transmissions in the cable network.
The noise resulting from ingress, commonly termed “ingress noise”, makes up a large percentage of the total noise found in many HFC networks. For example, ingress often occurs where the shielding, connectors, or terminations in the cable plant 21 are substandard or damaged. The source of the outside signal, which is commonly referred to as an “ingress source”, is often found on the subscriber's premises. For example, some examples common ingress sources include hair dryers, washing machines, vacuum cleaners, blenders, bread makers, remote control cars, cordless phones, ham radio, machinery, microwave ovens, and/or other devices at or near the same frequency as the RF signals. Unfortunately, since these ingress sources often create intermittent and/or seemingly random signals, ingress noise can be difficult to locate and/or track over time.
In general, the upstream or return path of a HFC network is more susceptible to ingress noise than the downstream path. One reason the upstream path is more susceptible is that it uses lower frequencies (e.g., upstream data is typically allocated to a CATV channel in the 5-42 MHz range, whereas downstream data is typically allocated to a CATV channel in the 50 MHz-1 GHz range), which increases the susceptibility to noise. Another reason the upstream path is more affected by ingress, is that all the subscriber's premises 28a, 28b, 28c utilize the same, relatively narrow upstream frequency range. Accordingly, ingress noise from various sources within the cable plant will combine as the signal propagates towards the headend (e.g., the hierarchical nature of a typical cable plant tends to increasingly concentrate and amplify ingress noise in the upstream path, resulting in a “funnel effect”, wherein the combined ingress noise at the headend is relatively high).
Reducing ingress noise and/or locating ingress sources is important to improving signal quality and/or improving the performance of the services that are being offered by the operator. Although operators have been monitoring noise in the upstream frequency band at the headend for years, just knowing that the noise exists does not aid in finding and fixing the ingress source. In fact, as a result of the “funnel effect” created by the combining nature of the CATV plant 21, it is very challenging to find ingress sources (e.g., which could be from any home, strand, or component on a node of the cable network identified as being affected by significant noise that is exceeding operator thresholds).
There have been several strategies employed by operators for finding and/or reducing ingress noise in the CATV plant. Since the upstream path is more susceptible and/or affected by ingress, these approaches typically involve monitoring the upstream communication path, herein referred to as the upstream path.
Perhaps the most common strategy is to begin looking for noise at a node identified as being affected by significant noise and then to traverse the network away from the headend until the source of the noise has been found and fixed. For example, one approach to locating an ingress source is to have a technician equipped with a handheld signal measurement device measure noise levels at each input of a first amplifier (e.g., bridger amplifier), to determine which input exhibits the highest level of noise. The technician then proceeds to a second amplifier, which is downstream from the first amplifier and is connected to the noisiest input of the first amplifier, and repeats the measurement to isolate a noisiest input of the second amplifier. In going from amplifier to amplifier, the technician travels to various locations in the field, repeating the measurements until the ingress source is finally located. Other approaches, which similarly use this type of iterative process commonly referred to as “noise segmentation”, involve sequentially disconnecting sections of the plant (e.g., to disconnect power to all amplifiers downstream of a selected amplifier) or using strategically placed low attenuation value switches, while monitoring variations in the noise profile at the headend. Unfortunately, due to the large number of subscriber premises served by each node and due to the fact that ingress noise is often intermittent, these trial and error process are extremely time consuming. For example, consider a weakness in a coax cable within a home that allows ingress into the plant. If this weakness is near a noisy appliance, such as a blender, the only time that noise is present is when the appliance is running. Accordingly, it is very common for a technician to be on a service call for a customer impacting, noise related issue when the noise is not present. Notably, operators have reported that they spend about 95% of their time localization ingress within their plant, and that 95% of the ingress is coming from the subscriber's premises.
Various methods have been proposed in order to reduce the amount of time technicians are in the field. For example, in U.S. Pat. No. 4,520,508 Reichert discloses a dedicated ingress noise monitor disposed at a remote node. The noise monitor measures a noise level at the node and provides information about the measured noise level by amplitude-modulating the return path signal. Unfortunately, since this approach requires the installation of autonomous noise meters, it is comparatively complex and costly.
In U.S. Pat. No. 7,489,641 by Miller et al., a test device disposed remotely from the headend is used to generate test data packets, which have a destination address of the test device itself. Accordingly, when the test data packets are transmitted to the headend, the headend automatically routes them back to the test device. The test packets are then received, demodulated, and analyzed by the test device for faults. Disadvantageously, the test apparatus of Miller et al. cannot distinguish exactly where ingress is occurring.
In U.S. Pat. Appl. Publ. No. 20050047442, Volpe et al. describe a test system that is configured to receive all upstream/downstream channels and demodulate upstream packets. A database of MAC/SID addresses is built, which allows the test system to eventually determine where the packets came from. Once the database is built, the origin of faulty data packets can be determined. Disadvantageously, the test system of Volpe lacks a capability to troubleshoot a particular upstream signal problem in real time.